(a) Field of the Invention
The present invention relates to an air volume adjustment knob of a spray gun, and more particularly, to one provides improved safety and easier operation.
(b) Description of the Prior Art
Whereas a spray gun of the prior art operates on the air supply from an external source and an adjustment knob is provided on the spray gun to regulate the air volume as the job requires. The adjustment knob found with spray guns generally available in the market, as illustrated in FIGS. 5 and 6 of the accompanying drawings is to provide at the rear end of a spray gun (A) an opening (A2) that is connected through an airway (A1). A reduced lateral hole (A3) is provided at the front end of the opening (A2) to merely allow the insertion of a control lever (A6) subject to the movement from a trigger (A5) of the spray gun (A) and the control lever (A6) penetrates through a leak proof sleeve (A7) screwed to the front end of the hole (A3). A sealing block (A61) is fixed to the rear end of the control lever (A6) to plug into and seal up the hole (A3) so that the hole (A3) is secluded from the opening (A2). The hole (A3) is connected to a longitudinally provided passage (A4) and connected through the outlet of a nozzle (A8). A knob structure (B) to adjust the air volume is provided in the rear end of the opening (A2). The knob structure is essentially comprised of a knob (B1) fixed to the top of a tube (B2) and a groove (B11) at an angle approximately of 270 degrees is provided in recess on the circumference of the knob (B1). The groove (B11) has its terminal secured and linked to the tube (B2), and a hole (B21) is provided in the tail of the tube (B2). When assembled, a spring (C) is placed into the tube (B2) of the knob (B1) and the tube (B2) is then inserted into the opening (A2) of the spray gun (A). A pin (D) is inserted into the spray gun (D) and rests in the groove (B11) of the knob (B1) thus to prevent the knob (B1) from being ejected. The inner end of the spring (C) holds against the sealing block (A61) of the control lever (A6) to block up the hole (A3). Once the spray gun (A) is in use, the knob (B1) is turned for the groove (B11) to move along the pin (D) for a certain angle thus to relatively drive the tube (B2) to merely have the hole (B21) in the tail of the tube (B2) to be aligned with the airway (A1). The trigger (A5) of the spray gun (A) is pulled to push the control lever (A6) inserted in the sleeve (A7) inside the opening (A2), and the sealing block (A61) is driven to push against the spring (C) and retreats from the hole (A3) to permit the air in the airway (A1) to flow through the hole (B21) in the tube (B2) into the opening (A2), where the air enters into the hole (A3) through a void formed as a result that the sealing block (A61) clears away from the hole (A3) and then flows through the path (A4) in the nozzle (A8) to provide the air required by the nozzle (A8).
However, the prior art is found with the following defectives. Reasons are first the knob structure is held in position essentially by having a pin with a very limited length of threaded tip to lock and hold against the groove of the knob thus to prevent the knob from escaping axially and to limit the turning angle of the knob. After use for a certain time, the pin is vulnerable to loosen up due to friction with the knob, which is frequently turned clockwise and counter-clockwise. The continuous supply of air also causes the knob to be easily ejected due to the return force of the spring and the air pressure. The ejected knob presents serious threaten to the safety of the holder of the spray gun. Furthermore, it is also a problem upon placing the tube containing the spring into the opening. As force must be continuously applied to compress the spring while aligning the groove in the knob to the pin before inserting and screwing in the pin, the force has to be applied in two directions at the same time, it becomes awkward for the holder of the spray gun and it is usually ejected by accident due to the return force of the spring.
The primary purpose of the present invention is to provide an air volume adjustment knob for a spray gun that is safe and easy to use. To achievement the purpose, in the rear end of the spray gun, an opening internally threaded, and connected through an airway is provided to accommodate a tube, a ring, a bonnet and a spring. Wherein, a hole is provided in the tube; a shaft containing a screwed hole is protruded from one end of the tube; a polygonal block is formed at the end of the shaft; a threaded section is provided on the outer wall of the ring; and a retaining hole corresponding to the shape of the polygonal block is formed axially in the bonnet. The ring is sleeved onto the shaft and secured to the opening of the spray gun by means of the threaded section of the ring. The bonnet is screwed to the tube with the retaining hole of the bonnet aligned to the polygonal block of the tube so that the tube is secured into the opening of the spray gun by the ring to adjust the output of the air volume through the hole of the tube as driven by the turning bonnet.